15th Edition
Understanding Computers
Today and Tomorrow
Comprehensive
Chapter 2
The Systems Unit:
Processing and Memory
Deborah Morley
Charles S. Parker
Copyright 2015 Cengage Learning
Learning Objectives
1. Understand how data and programs are represented to a
computer and be able to identify a few of the coding systems
used to accomplish this.
2. Explain the functions of the hardware components
commonly found inside the system unit, such as the CPU,
GPU, memory, buses, and expansion cards.
3. Describe how peripheral devices or other hardware can be
added to a computer.
4. Understand how a computer’s CPU and memory components
process program instructions and data.
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Learning Objectives
5. Name and evaluate several strategies that can be used today
for speeding up the operations of a computer.
6. List some processing technologies that may be used in future
computers.
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Overview
• Explain how computers represent data and program
instructions.
• Explain how the CPU and memory are arranged with other
components inside the system unit.
• Explain how a CPU performs processing tasks.
• Identify strategies that can be used today to create faster and
better computers in the future.
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Data and Program Representation
• Digital Data Representation
– Coding Systems
• Used to represent data and programs in a manner
understood by the computer
– Digital Computers
• Can only understand two states, off and on
(0 and 1)
– Digital Data Representation
• The process of representing
data in digital form so it can be
understood by a computer
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Digital Data Representation
– Bit
• The smallest unit of data that a
binary computer can recognize
(a single 1 or 0)
– Byte = 8 bits
• Byte terminology used to express
the size of documents and other
files, programs, etc.
– Prefixes are often used to express larger quantities of
bytes: kilobyte (KB), megabyte (MB), gigabyte (GB),
terabyte (TB), petabyte (PB), exabyte (EB), zettabyte (ZB),
yottabyte (YB).
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Representing Numerical Data
• The Binary Numbering System
– Numbering system
• A way of representing numbers
– Decimal numbering system
• Uses 10 symbols (0-9)
– Binary numbering system
• Uses only two symbols (1 and 0) to represent all
possible numbers
– In both systems, the position of the digits determines the
power to which the base number (such as 10 or 2) is raised
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Representing Numerical Data
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Coding Systems for Text-Based Data
• ASCII (American Standard Code for
Information Interchange)
– Coding system traditionally used
with personal computers
• EBCDIC (Extended Binary-Coded
Decimal Interchange Code)
– Developed by IBM, primarily for
mainframes
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Coding Systems for Text-Based Data
• Unicode
– Newer code (32 bits per character is common)
– Universal coding standard designed to represent textbased data written in any ancient or modern language
– Replacing ASCII as the primary text-coding system
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Coding Systems for Other Types of
Data
• Graphics Data (still images such as photos or drawings)
– Bitmapped images
• Image made of up of a grid of small dots called pixels
• Monochrome graphic can only be one of two colors
– Requires just one bit for color storage
• Images with more than two colors
– Can use 4, 8, or 24 bits to store the color data for
each pixel
– More bits = more colors
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Coding Systems for Other Types of
Data
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Coding Systems for Other Types of
Data
• Audio Data
– Must be in digital form in order to be stored on or
processed by a computer
– Often compressed when sent over the Internet
• MP3 files are 10 times smaller than their uncompressed
digital versions
• Download more quickly and take up less storage space
• Video Data
– Displayed using a collection of frames, each frame contains
a still image
– Amount of data can be substantial, but can be compressed
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Representing Software Programs
• Machine language
– Binary-based language for representing computer
programs the computer can execute directly
– Early programs were written in machine language
– Today’s programs still need to be translated into machine
language in order to be understood by the computer
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Quick Quiz
1. Another way to say “one million bytes” is
a. one kilobyte
b. one gigabyte
c. one megabyte
2. True or False: MP3 files are stored using 0s and 1s.
3. The _____________ numbering system is used by computers
to perform mathematical computations.
Answers:
1) c; 2) True; 3) binary
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Inside the System Unit
• System Unit
– The main case of a computer
– Houses the processing hardware for a computer
– Also contains storage devices, the power supply, and
cooling fans
– Houses processor, memory, interfaces to connect to
peripheral devices (printers, etc), and other components
– With a desktop computer, usually looks like a rectangular
box
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Inside the System Unit
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Inside the System Unit
• The Motherboard
– Computer Chip
• Very small pieces of silicon or other semi-conducting
material onto which integrated circuits are embedded
– Circuit Board
• A thin board containing computer chips and other
electronic components
– System Board
• The main circuit board inside the system unit to which
all devices must connect
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Inside the System Unit
• External devices (monitors, keyboards, mice, printers)
• Wireless devices (e.g., Bluetooth)
• Power Supply
– Connects to the motherboard to deliver electricity
(personal computer)
– Portable computers use rechargeable battery pack
• Nonremovable batteries more difficult and expensive
to replace
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Inside the System Unit
• Drive Bays
– Rectangular metal racks inside the system unit that house
storage devices
• Hard drive, CD/DVD drive, flash memory card reader
• Connected to the motherboard with a cable
• Processors
– The CPU (Central Processing Unit)
• Circuitry and components packaged together and connected
directly to the motherboard
• Does the vast majority of processing for a computer
• Also called a processor; called a microprocessor when talking
about personal computers
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Inside the System Unit
– Dual-core CPU
• Contains the processing components (cores) of two
separate processors on a single CPU
– Quad-core CPU
• Contains four cores
– Multi-core processors allow computers to work on more
than one task at a time
– Typically different CPUs for desktop computers, portable
computers, servers, mobile devices, consumer devices, etc.
• Personal computer CPU often made by Intel or AMD
• Media tablets and mobile phones use processors made
by other companies such as ARM
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Inside the System Unit
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Inside the System Unit
– The GPU (graphics processing unit)
• Takes care of the processing needed to display images
(including still images, animations) on the screen
• Can be located on
the motherboard,
on a video graphics
board, on in the
CPU package
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How It Works Box
GPUs and Transformers: The Ride 3D at Universal Studios
– Uses a 2,000 foot-long track, 14 huge screens, and 34
projectors
– Motion is synchronized with the action
– Images are 3D, 4K
– Used GPUs to see 3D
animations in real time
as they were being
developed
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Inside the System Unit
• Processing Speed
– CPU clock speed is one measurement of processing speed
– Rated in megahertz (MHz) or gigahertz (GHz)
– Higher CPU clock speed = more instructions processed per
second
– Alternate measure of processing speed is the number of
instructions a CPU can process per second
• Megaflops (millions), gigaflops (billions), teraflops
(trillions)
– Benchmark tests can be used to evaluate overall
processing speed
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Inside the System Unit
• Word Size
– The amount of data that a CPU can manipulate at one time
– Typically 32 or 64 bits
• Cache Memory
– Special group of very fast memory chips located on or
close to the CPU
– Level 1 is fastest, then Level 2, then Level 3
– More cache memory typically means faster processing
– Usually internal cache (built into the CPU)
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Inside the System Unit
• Bus Width, Bus Speed, and Bandwidth
– A bus is an electronic path over which data can
travel
– Found inside the CPU and on the motherboard
– Bus width is the number of wires in the bus over
which data can travel
• A wider bus allows more data to be transferred
at one time
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Inside the System Unit
• Bus width and speed determine
the throughput or bandwidth of
the bus
– The amount of data that can
be transferred by the bus in
a given time period
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Memory
• Memory
– Refers to chip-based storage located inside the system unit
– Storage refers to the amount of long-term storage
available to a computer
– Random Access Memory (RAM)
• Computer’s main memory
• Consists of chips arranged on a circuit board called a
memory module which are plugged into the
motherboard
• Stores essential parts of operating system, programs,
and data the computer is currently using
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Memory
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Memory
• Volatile
– RAM content lost when the computer is shut off
– ROM and flash memory are non-volatile
• Measured in bytes
– Amount installed depends on the CPU and
operating system being used
• Most personal computers use SD-RAM
• MRAM and PRAM - non-volatile RAM under
development
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Memory
• Each location in memory
has an address
– Each location
typically holds one
byte
– Computer system
sets up and
maintains directory
tables to facilitate
retrieval of the data
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Memory
– Registers
• High-speed memory built into the CPU
• Used to store data and intermediary results during
processing
• Fastest type of memory
– ROM (read-only memory)
• Non-volatile chips located on the motherboard into
which data or programs have been permanently stored
• Retrieved by the computer when needed
• Being replaced with flash memory
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Memory
– Flash Memory
• Nonvolatile memory chips that can be used for storage
• Have begun to replace ROM for storing system
information
• Now stores firmware for personal computers and other
devices
• Built into many types of devices (media tablets, mobile
phones, and digital cameras) for user storage
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Cooling Components
• Fans
– Fans used on most personal computers to help cool the
CPU and system unit
– Heat is an ongoing problem for CPU and computer
manufacturers
• Can damage components
• Cooler chips run faster
• Heat Sinks
– Small components typically made out of aluminum with
fins that help to dissipate heat
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Cooling Components
• Cooling Systems
– Liquid cooling systems
• Cool the computer with liquid-filled tubes
– Immersion cooling
• Hardware is actually submerged into units filled with a
liquid cooling solution
– Notebook cooling stand
• Cools the underside of a notebook computer
– Other cooling methods, such as ion pump cooling systems,
are under development
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Cooling Components
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Expansion
• Expansion Slots, Expansion Cards, and ExpressCard Modules
– Expansion Slot
• A location on the motherboard into which expansion
cards are inserted
– Expansion Card
• A circuit board inserted into an expansion slot
• Used to add additional functionality or to attach a
peripheral device
– ExpressCard Modules
• Designed to add additional functionality to notebooks
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Expansion
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Buses
• Bus
– An electronic path within a computer over which data travels
• Located within the CPU and etched onto the motherboard
– Expansion Bus
• Connects the CPU to peripheral (typically input and output)
devices
– Memory Bus
• Connects CPU directly to RAM
– Frontside Bus (FSB)
• Connects CPU to the chipset that connects the CPU to the
rest of the bus architecture
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Buses
– PCI and PCI Express (PCIe) Bus
• PCI has been one of the most common types
• Today, PCI Express bus, which is extremely fast, has
replaced the PCI bus
– Universal Serial Bus (USB)
• Extremely versatile
• Allows 127 different devices to connect to a computer
via a single USB port
– FireWire Bus
• Developed by Apple to connect multimedia devices to a
computer
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Ports and Connectors
• Port
– A connector on the exterior of a computer’s system unit to
which a device may be attached
– Typical desktop computer ports include:
• Power connector, Firewire, VGA monitor, Network, USB,
Audio, and HDMI
– Others include IrDA and Bluetooth ports, eSATA ports,
Thunderbolt ports (Apple devices)
– Most computers support the Plug and Play standard
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Ports and Connectors
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Ports and Connectors
– Portable computers have ports similar to desktop
computers, but often not as many
– Smartphones and mobile devices have more limited
expansion capabilities
• Usually have a USB port, HDMI port, and/or flash
memory card slot
• Flash memory cards often use the Secure Digital (SD)
format
• MiniSD and microSD cars are smaller than regular SD
cards
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Ports and Connectors
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Trend Box
Tablet Docks
– Used to help with tablet productivity
– Some are just a stand
– Many include a keyboard
– Some include ports (USB,
monitor, etc.) to connect
peripherals
– Some contain a battery
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Quick Quiz
1. Which type of memory is erased when the power goes out?
a. ROM
b. RAM
c. flash memory
2. True or False: The CPU can also be called the motherboard.
3. A(n) electronic path within a computer over which data travels
is called a(n) _____________.
Answers:
1) b; 2) False; 3) bus
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How the CPU Works
• CPU (Central Processing Unit)
– Consists of a variety of circuitry and components packaged
together
– Transistor: Key element of the microprocessor
• Made of semi-conductor material that acts like a switch
controlling the flow of electrons inside a chip
– Today’s CPUs contain hundreds of millions of transistors;
the number doubles about every 18 months (Moore’s Law)
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Inside the Industry Box
Moore’s Law
– In 1965, Gordon Moore
predicted that the number of
transistors per square inch on
chips had doubled every two
years and that trend would
continue
– Moore’s Law is still relevant
today for processors as well as
other computer components
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How the CPU Works
• Typical CPU Components
– Arithmetic/Logic Unit (ALU)
• Performs arithmetic involving integers and logical
operations
– Floating Point Unit (FPU)
• Performs decimal arithmetic
– Control Unit
• Coordinates and controls activities within a CPU core
– Prefetch Unit
• Attempts to retrieve data and instructions before they
are needed for processing in order to avoid delays
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How the CPU Works
– Decode Unit
• Translates instructions from the prefetch unit so they
are understood by the control unit, ALU, and FPU
– Registers and Internal Cache Memory
• Store data and instructions needed by the CPU
– Bus Interface Unit
• Allows the core to communicate with other CPU
components
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How the CPU Works
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The System Clock and the Machine
Cycle
• System Clock
– Small quartz crystal on the motherboard
– Timing mechanism within the computer system that
synchronizes the computer’s operations
• Sends out a signal on a regular basis to all computer
components
• Each signal is a cycle
• Number of cycles per second is measured in
hertz (Hz)
• One megahertz = one million ticks of the
system clock
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The System Clock and the Machine
Cycle
• Many PC system clocks run at 200 MHz
• Computers can run at a multiple or fraction of the
system clock speed
• A CPU clock speed of 2 GHz means the CPU clock
“ticks” 10 times during each system clock tick
• During each CPU clock tick, one or more pieces of
microcode are processed
• A CPU with a higher clock speed processes more
instructions per second than the same CPU with a
lower CPU clock speed
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The System Clock and the Machine
Cycle
• Machine Cycle
– The series of operations
involved in the execution of a
single machine level instruction
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Making Computers Faster and Better
Now and in the Future
• Improving the Performance of Your System Today
– Add more memory
– Perform system maintenance
• Uninstall programs properly
• Remove unnecessary programs
from the Startup list
• Consider placing large files not
needed on a regular basis on
external storage
• Delete temporary files
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Making Computers Faster and Better
Now and in the Future
• Error check and defrag the hard drive periodically
• Scan for viruses and spyware continually
• Clean out dust once or twice a year
– Buy a larger or second hard drive
– Upgrade your Internet connection
– Upgrade your video graphics card
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Making Computers Faster and Better
Now and in the Future
• Strategies for Making Faster and Better Computers
– Improved Architecture
• Smaller components, faster bus
speeds, multiple CPU cores,
support for virtualization
– Improved Materials
• Flexible electronic components
– Copper, high-k, graphene chip
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Making Computers Faster and Better
Now and in the Future
– Pipelining
• Allows multiple instructions to be processed at one
time
– Multiprocessing and Parallel Processing
• Use multiple processors to speed up processing
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Making Computers Faster and Better
Now and in the Future
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Future Trends
• Nanotechnology
– The science of creating tiny computers and components
less than 100 nanometers in size
– Carbon nanotubes (CNTs) used in many products today
– Nanofilters and nanosensors
– Future applications may be
built by working at the
individual atomic and
molecular levels
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Technology and You Box
“Magic” Glass
– MIT has developed nano-sized conical patterns on the
surface of glass to eliminated its reflective properties
– Glass resists fogging and is self-cleaning
– Possible uses:
• Smartphone screens
• Eyeglasses
• TVs
• Car windshieds
• Building windows
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Future Trends
• Quantum Computing
– Applies the principles of quantum physics and quantum
mechanics to computers
– Utilizes atoms or nuclei working together as quantum bits
(qubits)
– Qubits function simultaneously as the computer’s
processor and memory and can represent more than two
states
– Expected to be used for specialized applications, such as
encryption and code breaking
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Future Trends
• Optical Computing
– Uses light, from laser beams or infrared beams, to perform
digital computations
– Opto-electronic computers use both optical and electronic
components
• Silicon Photonics
– The process of making optical devices using silicon
manufacturing techniques
• Possible low-cost solution to future data-intensive
computing applications—telemedicine, cloud data
centers
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Future Trends
• Tera-Scale Computing
– The ability to process one trillion floating-point operations
per second (teraflops)
– Terascale research is focusing on creating multi-core
processors with tens to hundreds of cores
– Intel has created a Single-chip Cloud Computer which
contains 48 cores on one silicon chip
– Expected to be needed for future applications
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Future Trends
• 3D Chips
– Contain transistors that are
layered to cut down on the
surface area required
– Created by layering individual
silicon wafers on top of one
another
– Being used with memory, flash
memory, and CPUs
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Quick Quiz
1. Optical computers use which of the following to transmit and
process data?
a. Liquid
b. Light
c. Silicon
2. True or False: If your computer is running slowly, adding more
memory might speed it up.
3. A quantum bit is known as a(n) __________________.
Answers:
1) b; 2) True; 3) qubit
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Summary
•
•
•
•
Data and Program Representation
Inside the System Unit
How the CPU Works
Making Computers Faster and Better Now and in the Future
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